…the temporal order at which impulses from the brain and a peripheral nerve arrived at the spinal cord is critical to improving hand strength and dexterity among patients with a chronic, incomplete spinal cord injury.

Timing is everything when it comes to inducing plasticity, or adaptation, in the spinal cord to improve voluntary movement, according to researchers at the University of Pittsburgh School of Medicine. In a new study published, they demonstrated that the temporal order at which impulses from the brain and a peripheral nerve arrived at the spinal cord is critical to improving hand strength and dexterity among patients with a chronic, incomplete spinal cord injury.

The number of survivors after spinal cord injury has risen dramatically over the past few decades. More than 50 percent of all spinal cord injury survivors experienced cervical lesions, which often result in impairments in hand and arm motor function, explained senior author Monica A. Perez, Ph.D., assistant professor, of the Department of Physical Medicine and Rehabilitation and the Systems Neuroscience Institute, Pitt School of Medicine.

“We are using noninvasive electrophysiological measures to understand the mechanisms of recovery and to determine how we can best enhance transmission of remaining descending pathways to muscles in patients with incomplete spinal cord injuries,” she said. “The ultimate aim is to improve the patient’s ability to execute daily functions, such as eating and grasping, as independently as possible.”

In the study, lead author Karen L. Bunday, Ph.D., a postdoctoral research scholar in Dr. Perez’s lab, paired transcranial magnetic stimulation of the hand area of the brain’s motor cortex and electrical stimulation of a peripheral nerve in the wrist that innervates hand muscles in 19 participants with chronic cervical spinal cord injury and 14 uninjured participants. The paired pulses, which are noninvasive and painless, were given 100 times over approximately 17 minutes.

Unlike other stimulation techniques currently used in clinical studies, the researchers targeted the synapse, or junction, between corticospinal fibers and spinal motor neurons.

The researchers found that when impulses from the motor cortex were precisely timed to arrive at the spinal cord 1-2 milliseconds before impulses from a peripheral nerve in the wrist reached spinal motor neurons, there were improvements in hand muscle activity, strength, and manual dexterity in a precision grip task in spinal cord injured patients. They also observed an increase in corticospinal transmission in both injured and uninjured individuals that lasted for up to 80 minutes.

“We learned that we can noninvasively stimulate the brain and the peripheral nerve in a more efficient way,” Dr. Bunday said. “The timing between brain and peripheral nerve stimulation has to be precisely set in order to effectively improve voluntary movement. We customized the paired stimulation protocol to each person, which allowed us to take into account individual differences and conduction delays which are present after spinal cord injury.”

“We are now further examining the mechanisms of this plasticity and ways to make these changes more persistent,” Dr. Perez said. “In the future, this could provide a basis for developing some devices that people could take home and use to strengthen residual spinal cord synaptic connections to enhance muscle function.”